In the manufacturing process of a liquid crystal substrate, it is necessary to prebake polyimide (PI) liquid on a glass substrate. In the baking process, generally the glass substrate is irradiated by infrared rays and heated to a certain temperature, so that solvent in the PI liquid is evaporated, with a result that the concentration of PI is increased. In the above-mentioned baking process, the glass substrate is generally supported by lift pins or supporting pins. However, the material for the lift pins or supporting pins is not absolutely thermally-insulated, and thus difference of heat conduction rates exists between areas where the glass substrate is in contact with the lift pins or the supporting pins and non-contacting areas (i.e., areas where the glass substrate is not in contact with the lift pins or the supporting pins). Therefore, the glass substrate cannot be heated uniformly, causing mura defects appear on the glass substrate. Consequently, the yield of acceptable glass substrates is reduced.
FIG. 4 to FIG. 6 show a device for baking a substrate in the prior art. With reference to FIG. 4 and FIG. 5, the device for baking the glass substrate in the prior art includes a hot plate 1′ and a plurality of lift pins 2′. Holes through which the lift pins 2′ can pass are formed in the hot plate 1′. The lift pins 2′ extend through the hot plate 1′ via the holes and then support a glass substrate 3′ to be heated. The prior art has the following defects. With reference to FIG. 6, hot air is sprayed to the back side of display areas (chip AA areas) 3.1′ through the holes for the lift pins during heating, so that temperature difference or non-uniform heating exists between the display areas corresponding to the holes (elliptical areas in the glass substrate 3′) and the remaining areas. Therefore, as shown in FIG. 5, mura defects corresponding to the supporting positions of the lift pins 2′ on the glass substrate 3′ appear in the display areas 3.1′ of the glass substrate 3′. Consequently, the quality and yield of the glass substrate are affected.